The vertebrae in a patient's spinal column are linked to one another by an intevertebral disc and facet joints. This three joint complex controls the movement of the vertebrae relative to one another. Each vertebra has a pair of articulating surfaces located on its left side, and a pair of articulating surfaces located on its right side, and each pair includes a superior articular surface and an inferior articular surface. Together the superior and inferior articular surfaces of adjacent vertebrae form a facet joint. Facet joints are synovial joints, which means that each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. The joint surfaces are coated with cartilage that allow the joints to move or articulate relative to one another.
Diseased, degenerated, impaired, or otherwise painful facet joints and/or discs can require surgery to stabilize the spine and relieve pain in the three joint complex. In the lumbar spine, for example, one form of treatment to stabilize the spine and relieve pain involves fusion of the facet joint.
One known technique for stabilizing and treating the facet joint involves a trans-facet fusion, in which pins, screws or bolts penetrate the lamina to fuse the joint. Such a technique has associated with it the risk of further injury to the patient, as such translamina facet instrumentation can be difficult to place in such a way that it does not violate the spinal canal and/or contact the dura of the spinal cord or the nerve root ganglia. Further, trans-facet instrumentation has been known to create rotational distortion, lateral offset, hyper-lordosis, and/or intervertebral foraminal stenosis at the level of instrumentation.
Examples of facet instrumentation currently used to stabilize the lumbar spine include trans-lamina facet screws (“TLFS”) and trans-facet pedicle screws (“TFPS”). TLFS and TFPS implants provide reasonable mechanical stability, but, as noted above, they can be difficult to place, have long trajectories, and surgical access can be confounded by local anatomy. In some instances, these implants can result in some degree of foraminal stenosis.
US Patent Publication 2008-0255622 (DePuy Spine), the specification of which is incorporated by reference in its entirety, discloses spinal implants and methods relating to stabilization and/or fusion of a facet joint via trans-facet and intra-facet delivery of the implants. In general, the implant functions as a sort of mechanical staple and/or key that prevents sliding motion between the diarthroidal surfaces of the facet joint. Further, the spinal implant can include a fusion-promoting bioactive material thereby providing for a single spinal implant capable of allowing for both fixation and fusion of a desired facet joint. In particular, it discloses facet fixation and fusion washer and screw assemblies.
It is an object of the present invention to prepare the spinal upper facet to facilitate insertion of such combined screw/washer implants, thereby preventing bone damage and facet weakening, and also allowing the placing of graft therein so as to maximize implant stabilization.
The art discloses a number of bone reamers.
U.S. Pat. No. 7,008,430 (Dong) discloses a positioning tool for a joint socket cutting instrument or an implant for use with a minimally invasive surgical procedure and in conjunction with a computer assisted surgical procedure. The positioning tool has a longitudinally extending drive shaft having a moveable joint at a first end and a drive coupling for connecting to a power source at a second end. A holder for mounting a cutting tool such as a drill or as an acetabular cutting instrument or for mounting an acetabular implant is coupled to the moveable joint at the first end of the drive shaft for movement with respect to the drive shaft. The holder is rotatable about a central axis thereof when the drive shaft is rotated. The drive shaft includes a shaft bearing mounted thereon which is pivotally coupled to the shaft at a fixed longitudinal position and is pivotally coupled to a longitudinally extending first arm having a handle. A tracker system which is capable of being utilized by a computer-aided surgical system is mounted on the first arm. A second arm is provided which is pivotally connected to the holder at a first end and pivotally connected to the first arm at a second end. The resulting four bar linkage allows the holder and the cutting instrument/implant to be manipulated in any position while the known geometric relationship between the tracker and the holder allows the location of the holder to be displayed by the computer on a cathode ray tube with respect to a joint.
PCT Patent Publication WO 2006/105000 (Chervitz) discloses a reamer designed to engage a guide member, such as a guide wire, implanted in bone at any of a plurality of relative orientations such that the resulting resection of the bone does not depend on the relative orientation. The reamer may have a shaft that receives torque and a reaming head with a cavity into which a protruding portion of the guide wire is insertable. The cavity may have a generally conical shape capable of receiving the guide wire at a variety of relative orientations. The orientation of the reaming head is determined not by that of the guide wire, but by a stationary frame to which the reamer is coupled. The reamer may optionally have an offset assembly that causes the reaming head to rotate about an axis displaced from that of the shaft to reduce the size of the incision required to reaming head.
U.S. Pat. No. 7,553,313 (Bagby) discloses an apparatus for preparing a spinal implant surgical site for receiving a spinal fusion implant. The apparatus includes a drive shaft, a handle, and a hollow, cylindrical cutting body. The handle is carried by the drive shaft, the hollow, cylindrical cutting body is provided at a leading end of the drive shaft. The cylindrical cutting body has an open leading end, a plurality of circumferentially spaced-apart cutting teeth provided on the open leading end, and a plurality of circumferentially spaced-apart gullets each provided between an adjacent pair of the cutting teeth.